Emphasis for the coming year will entail further studies on: 1. Evidence for a non-splenic platelet pool which is rapidly mobilizable with exercise or epinephrine. 2. Evidence that megathrombocyte number determines platelet function. 3. Development of a simple technique for the direct measurement of anti-platelet antibody bound to platelets. 4. Evidence that anti-platelet antibody may be a disease where antibody is directed against other tissues as well as platelets. BIBLIOGRAPHIC REFERENCES: Freedman, M.L. and Karpatkin, S., Heterogeneity of Rabbit Platelets. IV. Thrombocytosis with Absolute Megathrombocytosis in Phenylhydrazine-induced Hemolytic Anemia in Rabbits. Thromb. Diath. Haemorrh. 33:335, 1975. Verp, M. and Karpatkin, S., Effect of plasma, steroids, and steroid products on the adhesion of human thrombocytes to human leukocytes. J. Lab. Clin. Med. 85:478, 1975.